1. Field of the Invention
The invention relates to an apparatus for feeding an electrical load having a predetermined nominal voltage, comprising an input for connection to a supply voltage source and an output for the load.
2. Description of Related Art
Such an apparatus, in its simplest form, consists of a mechanical switch for closing a circuit connecting a supply voltage source, e.g. a battery or the electric network, to the load. The load most typically is an incandescent bulb. The circuit may contain in addition a fuse against overload.
By way of specific measures in circuit technology, the load may be fed with more or less energy in order to control for example the brightness of an incandescent bulb from 0 per cent to 100 per cent. This is effected e.g. with the aid of a potentiometer. Commonly used at present are so-called phase-angle controls with thyristors or triacs connecting each half-wave of an alternating voltage to the load at a delayed, selectable moment of time.
Feeding of an electrical load with direct current and feeding of an electrical load with alternating current each involve advantages and disadvantages. Attempts have been made specifically with incandescent bulbs and other illumination devices to obtain an increased luminosity factor or light yield (with a given electrical power) by improving the efficiency.
For feeding electrical loads it is known in particular also with stepping motors or the like to apply a pulse-shaped supply voltage to the load, with the duty cycle of the pulse train, i.e. the ratio of pulse width to pulse spacing or interval, determining the power supplied to the load from 0 to 100 per cent. In the extreme case of such pulse-shaped feeding, pure direct current is fed to the load. The pulse width then is 100 per cent, whereas the interval is 0 per cent, corresponding to a duty cycle (pulse/interval) of infinity. The voltage amplitude of the voltage pulses must in each case correspond to the nominal voltage of the load.